Method for transmitting a sounding reference signal in a wireless communication system, and apparatus for same

ABSTRACT

A method for receiving an aperiodic sounding reference signal (SRS) from a user equipment (UE) at a base station in a time division duplex (TDD) communication system. The method according to one embodiment includes transmitting downlink control information (DCI) including a request of the aperiodic SRS to the UE. The downlink control information includes information for receiving downlink data using multiple antennas from the base station by the user equipment. The method according to the embodiment further includes receiving the aperiodic SRS from the UE in response to the request.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 13/497,293 filed Jul. 23, 2012, which is the national phase ofPCT International Application No. PCT/KR2010/006475 filed Sep. 20, 2010,which claims the benefit of U.S. Provisional Application Nos. 61/244,424filed on Sep. 21, 2009, 61/310,712 filed Mar. 5, 2010, and 61/316,820filed on Mar. 23, 2010. The entire contents of all of the aboveapplications are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless communication system, andmore particularly, to a method and apparatus for transmitting anaperiodic sounding reference signal from a user equipment to a basestation in a wireless communication system.

2. Discussion of the Related Art

As an example of a mobile communication system to which the presentinvention is applicable, a 3^(rd) Generation Partnership Project (3GPP)Long Term Evolution (LTE) communication system will be schematicallydescribed.

FIG. 1 is a diagram showing a network structure of an Evolved UniversalMobile Telecommunications System (E-UMTS) as a mobile communicationsystem. The E-UMTS is an evolved form of the UMTS and has beenstandardized in the 3GPP. Generally, the E-UNITS may be called a LongTerm Evolution (LTE) system. For details of the technical specificationsof the UMTS and E-UMTS, refer to Release 7 and Release 8 of “3^(rd)Generation Partnership Project; Technical Specification Group RadioAccess Network”.

Referring to FIG. 1, the E-UMTS mainly includes a User Equipment (UE)120, base stations (or eNBs or eNode Bs) 110 a and 110 b, and an AccessGateway (AG) which is located at an end of a network (E-UTRAN) and whichis connected to an external network. Generally, an eNB cansimultaneously transmit multiple data streams for a broadcast service, amulticast service and/or a unicast service.

One or more cells may exist per eNB. The cell is set to use a bandwidthsuch as 1.25, 2.5, 5, 10, 15 or 20 MHz to provide a downlink or uplinktransmission service to several UBs. Different cells may be set toprovide different bandwidths. The eNB controls data transmission orreception of a plurality of UEs. The eNB transmits downlink (DL)scheduling information of DL data so as to inform a corresponding UE oftime/frequency domain in which data is transmitted, coding, data size,and Hybrid Automatic Repeat and reQest (HARQ)-related information. Inaddition, the eNB transmits uplink (UL) scheduling information of ULdata to a corresponding UE so as to inform the UE of a time/frequencydomain which may be used by the UE, coding, data size and HARQ-relatedinformation. An interface for transmitting user traffic or controltraffic can be used between eNBs. A Core Network (CN) may include the AGand a network node or the like for user registration of the UE. The AGmanages mobility of a UE on a Tracking Area (TA) basis. One TA includesa plurality of cells.

Although wireless communication technology has been developed up to LongTerm Evolution (LTE) based on Wideband Code Division Multiple Access(WCDMA), the demands and the expectations of users and providerscontinue to increase. In addition, since other radio access technologieshave been continuously developed, new technology evolution is requiredto secure high competitiveness in the future. Decrease in cost per bit,increase in service availability, flexible use of a frequency band,simple structure, open interface, suitable User Equipment (UE) powerconsumption and the like are required.

Recently, the standardization of the subsequent technology of the LTE isongoing in the 3GPP. In the present specification, the above-describedtechnology is called “LTE-Advanced” or “LTE-A”. The LIE system and theLTE-A system are different from each other in terms of system bandwidth.The LIE-A system aims to support a wide bandwidth of a maximum of 100MHz. The LIE-A system uses carrier aggregation or bandwidth aggregationtechnology which achieves the wide bandwidth using a plurality offrequency blocks. The carrier aggregation enables the plurality offrequency blocks to be used as one large logical frequency band in orderto use a wider frequency band. The bandwidth of each of the frequencyblocks may be defined based on the bandwidth of a system block used inthe LTE system. Each frequency block is transmitted using a componentcarrier.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method and apparatusfor transmitting an aperiodic sounding reference signal from a userequipment to a base station in a wireless communication system.

The technical problems solved by the present invention are limited tothe above technical problems and those skilled in the art may understandother technical problems from the following description.

The object of the present invention can be achieved by providing amethod for transmitting an aperiodic sounding reference signal (SRS) ata user equipment in a wireless communication system including receivingdownlink control information from a base station, decoding a downlinkcontrol information (DCI) format for downlink transmission included inthe downlink control information, checking an instruction to transmitthe aperiodic SRS in the DCI format for downlink transmission, andtransmitting the aperiodic SRS to the base station according to theinstruction. If the downlink control channel is received via an n^(th)subframe, the aperiodic SRS may be transmitted via an (n+k)^(th)subframe (k≧4).

The method may further include receiving a transmission parameter of theaperiodic SRS through a higher layer. The DCI format for downlinktransmission may include a transmission parameter of the aperiodic SRS.The DCI format for downlink transmission may be a DCI format for amultiple input multiple output (MIMO) system.

In another aspect of the present invention, there is provided a userequipment in a wireless communication system including a receptionmodule configured to receive downlink control information from a basestation, a processor configured to decode a downlink control information(DCI) format for downlink transmission included in the downlink controlinformation and check an instruction to transmit the aperiodic SRS inthe DCI format for downlink transmission, and a transmission moduleconfigured to transmit an aperiodic SRS to the base station according tothe instruction. If the downlink control channel is received via ann^(th) subframe, the aperiodic SRS may be transmitted via an (n+k)^(th)subframe k≧4).

The reception module may receive a transmission parameter of theaperiodic SRS through a higher layer. The DCI format for downlinktransmission may include a transmission parameter of the aperiodic SRS.The DCI format for downlink transmission may be a DCI format for amultiple input multiple output (MIMO) system.

According to the embodiments of the present invention, it is possible toefficiently transmit an aperiodic sounding reference signal from a userequipment to a base station in a wireless communication system.

The effects of the present invention are not limited to theabove-described effects and other effects which are not described hereinwill become apparent to those skilled in the art from the followingdescription.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a network structure of an Evolved UniversalMobile Telecommunications System (E-UMTS) as an example of a mobilecommunication system.

FIG. 2 is a diagram showing a control plane and a user plane of a radiointerface protocol architecture between a User Equipment (UE) and anEvolved Universal Terrestrial Radio Access Network (E-UTRAN) based on a3^(rd) Generation Partnership Project (3GPP) radio access networkstandard.

FIG. 3 is a diagram showing physical channels used in a 3GPP system anda general signal transmission method using the same.

FIG. 4 is a diagram showing the structure of a radio frame used in aLong Term Evolution (LTE) system.

FIG. 5 is a diagram showing the structure of an uplink subframe in anLTE system.

FIG. 6 is a block diagram showing a transmitter or receiver according toan embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The configuration, operation and other features of the present inventionwill be understood by the embodiments of the present invention describedwith reference to the accompanying drawings. The following embodimentsare examples of applying the technical features of the present inventionto a 3^(rd) Generation Partnership Project (3GPP) system.

Hereinafter, a system in which a system band uses a single frequencyblock is referred to as a legacy system or a narrowband system. A systemin which a system band includes a plurality of frequency blocks and atleast one frequency blocks are used as a system block of a legacy systemis referred to as an evolved system or wideband system. The frequencyblock used as the legacy system block has the same size as the systemblock of the legacy system. The sizes of the remaining frequency blocksare not specially limited. However, in order to simplify a system, thesize of the remaining frequency blocks may be determined based on thesize of the system block of the legacy system. For example, a 3GPP LIEsystem and a 3GPP LTE-A system are evolved from a legacy system.

Based on the above definition, in the present specification, a 3GPP LIEsystem is called an LIE system or a legacy system. A user equipment (UE)which supports an LIE system is called an LIE UE or a legacy UE. A 3GPPLIE-A system is called an LIE-A system or an evolved system. A UE whichsupports an LTE-A system is called an LTE-A UE or an evolved UE.

Although, for convenience, the embodiments of the present invention aredescribed using the LIE system and the LIE-A system in the presentspecification, the embodiments of the present invention are applicableto any communication system corresponding to the above definition. Inaddition, although the embodiments of the present invention aredescribed based on a Frequency Division Duplex (FDD) scheme in thepresent specification, the embodiments of the present invention may beeasily modified and applied to a Half-Duplex FDD (H-FDD) scheme or aTime Division Duplex (TDD) scheme.

FIG. 2 shows a control plane and a user plane of a radio interfaceprotocol between a UE and an Evolved Universal Terrestrial Radio AccessNetwork (E-UTRAN) based on a 3GPP radio access network standard. Thecontrol plane refers to a path used for transmitting control messagesused for managing a call between the UE and the network. The user planerefers to a path used for transmitting data generated in an applicationlayer, e.g., voice data or Internet packet data.

A physical (PHY) layer of a first layer provides an information transferservice to a higher layer using a physical channel. The PHY layer isconnected to a Medium Access Control (MAC) layer located on a higherlayer via a transport channel. Data is transported between the MAC layerand the PHY layer via the transport channel. Data is also transportedbetween a physical layer of a transmitting side and a physical layer ofa receiving side via a physical channel. The physical channel uses atime and a frequency as radio resources. More specifically, the physicalchannel is modulated using an Orthogonal Frequency Division MultipleAccess (OFDMA) scheme in downlink and is modulated using aSingle-Carrier Frequency Division Multiple Access (SC-FDMA) scheme inuplink.

A Medium Access Control (MAC) layer of a second layer provides a serviceto a Radio Link Control (RLC) layer of a higher layer via a logicalchannel. The RLC layer of the second layer supports reliable datatransmission. The function of the RLC layer may be implemented by afunctional block within the MAC. A Packet Data Convergence Protocol(PDCP) layer of the second layer performs a header compression functionto reduce unnecessary control information for efficient transmission ofan Internet Protocol (IP) packet such as an IPv4 packet or an IPv6packet in a radio interface having a relatively small bandwidth.

A Radio Resource Control (RRC) layer located at the bottom of a thirdlayer is defined only in the control plane and is responsible forcontrol of logical, transport, and physical channels in association withconfiguration, re-configuration, and release of Radio Bearers (RBs). TheRB is a service that the second layer provides for data communicationbetween the UE and the network. To accomplish this, the RRC layer of theUE and the RRC layer of the network exchange RRC messages. The UE is inan RRC connected mode if an RRC connection has been established betweenthe RRC layer of the radio network and the RRC layer of the UE.Otherwise, the UE is in an RRC idle mode. A Non-Access Stratum (NAS)layer located above the RRC layer performs functions such as sessionmanagement and mobility management.

One cell of the eNB is set to use a bandwidth such as 1.25, 2.5, 5, 10,15 or 20 MHz to provide a downlink or uplink transmission service toseveral UEs. Different cells may be set to provide different bandwidths.

Downlink transport channels for transmission of data from the network tothe UE include a Broadcast Channel (BCH) for transmission of systeminformation, a Paging Channel (PCH) for transmission of paging messages,and a downlink Shared Channel (SCH) for transmission of user traffic orcontrol messages. Traffic or control messages of a downlink multicast orbroadcast service may be transmitted through a downlink SCH and may alsobe transmitted through a downlink multicast channel (MCH). Uplinktransport channels for transmission of data from the UE to the networkinclude a Random Access Channel (RACH) for transmission of initialcontrol messages and an uplink SCH for transmission of user traffic orcontrol messages. Logical channels, which are located above thetransport channels and are mapped to the transport channels, include aBroadcast Control Channel (BCCH), a Paging Control Channel (PCCH), aCommon Control Channel (CCCH), a Multicast Control Channel (MCCH), and aMulticast Traffic Channel (MTCH).

FIG. 3 is a diagram showing physical channels used in a 3GPP system anda general signal transmission method using the same.

A UE performs an initial cell search operation such as synchronizationwith an eNB when power is turned on or the UE enters a new cell (S301).The UE may receive a Primary Synchronization Channel (P-SCH) and aSecondary Synchronization Channel (S-SCH) from the eNB, performsynchronization with the eNB, and acquire information such as a cell ID.Thereafter, the UE may receive a physical broadcast channel from the eNBso as to acquire broadcast information within the cell. Meanwhile, theUE may receive a Downlink Reference Signal (DL RS) so as to confirm adownlink channel state in the initial cell search step.

The UE which completes the initial cell search may receive a PhysicalDownlink Control Channel (PDCCH) and a Physical Downlink Shared Channel(PDSCH) according to information included in the PDCCH so as to acquiremore detailed system information (S302).

Meanwhile, if the eNB is initially accessed or radio resources forsignal transmission are not present, the UE may perform a Random AccessProcedure (RACH) (step S303 to S306) with respect to the eNB. In thiscase, the UE may transmit a specific sequence through a Physical RandomAccess Channel (PRACH) as a preamble (S303 and S305), and receive aresponse message of the preamble through the PDCCH and the PDSCHcorresponding thereto (S304 and S306). In the case of contention-basedRACH, a contention resolution procedure may be further performed.

The UE which performs the above procedures may perform PDCCH/PDSCHreception (S307) and Physical Uplink Shared Channel PUSCH)/PhysicalUplink Control Channel (PUCCH) transmission (S308) as a generaluplink/downlink signal transmission procedure. The control informationtransmitted from the UE to the eNB in uplink or transmitted from the eNBto the UE in downlink includes a downlink/uplink ACK/NACK signal, aChannel Quality indicator (CQI), a Precoding Matrix Index (PMI), a RankIndicator (RI), and the like. In the case of the 3GPP LTE system, the UEmay transmit the control information such as CQI/PMI/RI through thePUSCH and/or the PUCCH.

FIG. 4 is a diagram showing the structure of a radio frame used in aLong Term Evolution (LTE) system.

Referring to FIG. 4, the radio frame has a length of 10 ms(327200·T_(s)) and includes 10 subframes with the same size. Each of thesubframes has a length of 1 ms and includes two slots. Each of the slotshas a length of 0.5 ms (15360·T_(s)). T_(s) denotes a sampling time, andis represented by T_(s)=1/(15 kHz×2048)=3.2552×10⁻⁸ (about 33 ns). Eachslot includes a plurality of OFDM or SC-FDMA symbols in a time domain,and includes a plurality of resource blocks (RBs) in a frequency domain.In the LTE system, one RB includes 12 subcarriers×7(6) OFDM or SC-FDMAsymbols. A Transmission Time Interval (TTI) which is a unit time fortransmission of data may be determined in units of one or moresubframes. The structure of the radio frame is only exemplary and thenumber of subframes included in the radio frame, the number of slotsincluded in the subframe, or the number of OFDM or SC-FDMA symbolsincluded in the slot may be variously changed.

FIG. 5 is a diagram showing the structure of an uplink subframe in anLTE system.

Referring to FIG. 5, a subframe 500 having a length of 1 ms, which is abasic unit of LTE uplink transmission, includes two slots 501 eachhaving a length of 0.5 ms. In case of normal cyclic prefix (CP), eachslot includes seven symbols 502 and one symbol corresponds to oneSC-FDMA symbol. An RB 503 is a resource allocation unit corresponding to12 subcarriers in a frequency domain and one slot in a time domain. Thestructure of the uplink subframe of the LTE is roughly divided into adata region 504 and a control region 505. The data region refers to aseries of communication resources used to transmit data such as voice orpackets to each UE and corresponds to resources excluding resourcesbelonging to the control region in a subframe. The control region refersto a series of communication resources used to transmit a downlinkchannel quality report from each UE, reception ACK/NACK for a downlinksignal, an uplink scheduling request, etc.

As shown in FIG. 5, a region 506 for transmitting a sounding referencesignal (SRS) within one subframe is a part including SC-FDMA symbolslocated at the last of a time axis in one subframe and the SRS istransmitted via a data transmission band on a frequency axis. SRSs ofseveral UEs transmitted using the last SC-FDMA symbols of the samesubframe may be distinguished according to frequency positions.

The SRS is composed of constant amplitude zero auto correlation (CAZAC)sequences. SRSs transmitted from several UEs are CAZAC sequencesr^(SRS)(n)=r_(u,v) ^((a))(n) having different cyclic shift values αaccording to Equation 1.

$\begin{matrix}{\alpha = {2\pi \frac{n_{SRS}^{cs}}{8}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

where, n_(SRS) ^(cs) is a value set to each UE by a higher layer and hasan integer value of 0 to 7. Accordingly, the cyclic shift value may haveeight values according to n_(SRS) ^(cs).

CAZAC sequences generated from one CAZAC sequence through cyclic shifthave zero correlation values with sequences having different cyclicshift values. Using such property, SRSs of the same frequency domain maybe divided according to CAZAC sequence cyclic shift values. The SRS ofeach UE is allocated to the frequency according to a parameter set bythe eNB. The UE performs frequency hopping of the SRS so as to transmitthe SRS with an overall uplink data transmission bandwidth.

Hereinafter, a detailed method of mapping physical resources fortransmitting SRSs in an LTE system will be described.

In order to satisfy transmit power P_(SRS) of a UE, an SRS sequencer^(SRS)(n) is first multiplied by an amplitude scaling factor β_(SRS)and is then mapped to a resource element (RE) having an index (k, l)from r^(SRS)(0) by Equation 2.

$\begin{matrix}{\alpha_{{{2\; k} + k_{0}},l} = \left\{ \begin{matrix}{\beta_{SRS}{r^{SRS}(k)}} & {{k = 0},1,\ldots \mspace{14mu},{M_{{sc},b}^{RS} - 1}} \\0 & {otherwise}\end{matrix} \right.} & {{Equation}\mspace{14mu} 2}\end{matrix}$

where, k₀ denotes a frequency domain start point of an SRS and isdefined by Equation 3.

$\begin{matrix}{k_{0} = {k_{0}^{\prime} + {\sum\limits_{b = 0}^{B_{SRS}}\; {2\; M_{{sc},b}^{RS}n_{b}}}}} & {{Equation}\mspace{14mu} 3}\end{matrix}$

where, n_(b) denotes a frequency position index. k′₀ for a generaluplink subframe is defined by Equation 4 and k′₀ for an uplink pilottime UpPTS is defined by Equation 5.

$\begin{matrix}{\mspace{79mu} {k_{0}^{\prime} = {{\left( {\left\lfloor {N_{RB}^{UL}/2} \right\rfloor - {m_{{SRS},0}/2}} \right)N_{SC}^{RB}} + k_{TC}}}} & {{Equation}\mspace{14mu} 4} \\{k_{0}^{\prime} = \left\{ \begin{matrix}{{\left( {N_{RB}^{UL} - m_{{SRS},0}^{\max}} \right)N_{sc}^{RB}} + k_{TC}} & \begin{matrix}{{if}\mspace{14mu} \left( {{\left( {n_{f}{mod}\; 2} \right) \times \left( {2 - N_{SP}} \right)} + n_{hf}} \right)} \\{{{mod}\; 2} = 0}\end{matrix} \\k_{TC} & {otherwise}\end{matrix} \right.} & {{Equation}\mspace{14mu} 5}\end{matrix}$

In Equations 4 and 5, k_(TC) denotes a transmissionComb parametersignaled to a UE via a higher layer and has a value of 0 or 1. Inaddition, n_(hf) is 0 in an uplink pilot time slot of a first half frameand is 0 in an uplink pilot slot of a second half frame. M_(sc,b) ^(RS)is the length, that is, the bandwidth, if the SRS sequence expressed insubcarrier units defined by Equation 6.

M _(sc,b) ^(RS) =m _(SRS,b) N _(sc) ^(RB)/2  Equation 6

In Equation 6, m_(SRS,b) is a value signaled from an eNB according to anuplink bandwidth N_(RB) ^(UL) as shown in Tables 1 to 4.

In order to acquire m_(SRS,b), a cell-specific parameter C_(SRS) havingan integer value of 0 to 7 and a UE-specific parameter B_(SRS) having aninteger value of 0 to 3 are necessary. The values of C_(SRS) and B_(SRS)are provided by a higher layer.

TABLE 1 b_(hop) = 0, 1, 2, 3 and 6 ≦ N_(RB) ^(UL) ≦ 40 SRS SRS- SRS-SRS- SRS- bandwidth Bandwidth Bandwidth Bandwidth Bandwidthconfiguration B_(SRS) = 0 B_(SRS) = 1 B_(SRS) = 2 B_(SRS) = 3 C_(SRS)m_(SRS,b) N_(b) m_(SRS,b) N_(b) m_(SRS,b) N_(b) m_(SRS,b) N_(b) 0 36 112 3 4 3 4 1 1 32 1 16 2 8 2 4 2 2 24 1 4 6 4 1 4 1 3 20 1 4 5 4 1 4 1 416 1 4 4 4 1 4 1 5 12 1 4 3 4 1 4 1 6 8 1 4 2 4 1 4 1 7 4 1 4 1 4 1 4 1

TABLE 2 b_(hop) = 0, 1, 2, 3 and 40 < N_(RB) ^(UL) ≦ 60 SRS SRS- SRS-SRS- SRS- bandwidth Bandwidth Bandwidth Bandwidth Bandwidthconfiguration B_(SRS) = 0 B_(SRS) = 1 B_(SRS) = 2 B_(SRS) = 3 C_(SRS)m_(SRS,0) N₀ m_(SRS,1) N₁ m_(SRS,2) N₂ m_(SRS,3) N₃ 0 48 1 24 2 12 2 4 31 48 1 16 3 8 2 4 2 2 40 1 20 2 4 5 4 1 3 36 1 12 3 4 3 4 1 4 32 1 16 28 2 4 2 5 24 1 4 6 4 1 4 1 6 20 1 4 5 4 1 4 1 7 16 1 4 4 4 1 4 1

TABLE 3 b_(hop) = 0, 1, 2, 3 and 60 < N_(RB) ^(UL) ≦ 80 SRS SRS- SRS-SRS- SRS- bandwidth Bandwidth Bandwidth Bandwidth Bandwidthconfiguration B_(SRS) = 0 B_(SRS) = 1 B_(SRS) = 2 B_(SRS) = 3 C_(SRS)m_(SRS,0) N₀ m_(SRS,1) N₁ m_(SRS,2) N₂ m_(SRS,3) N₃ 0 72 1 24 3 12 2 4 31 64 1 32 2 16 2 4 4 2 60 1 20 3 4 5 4 1 3 48 1 24 2 12 2 4 3 4 48 1 163 8 2 4 2 5 40 1 20 2 4 5 4 1 6 36 1 12 3 4 3 4 1 7 32 1 16 2 8 2 4 2

TABLE 4 b_(hop) = 0, 1, 2, 3 and 80 < N_(RB) ^(UL) ≦ 110 SRS SRS- SRS-SRS- SRS- bandwidth Bandwidth Bandwidth Bandwidth Bandwidthconfiguration B_(SRS) = 0 B_(SRS) = 1 B_(SRS) = 2 B_(SRS) = 3 C_(SRS)m_(SRS,0) N₀ m_(SRS,1) N₁ m_(SRS,2) N₂ m_(SRS,3) N₃ 0 96 1 48 2 24 2 4 61 96 1 32 3 16 2 4 4 2 80 1 40 2 20 2 4 5 3 72 1 24 3 12 2 4 3 4 64 1 322 16 2 4 4 5 60 1 20 3 4 5 4 1 6 48 1 24 2 12 2 4 3 7 48 1 16 3 8 2 4 2

As described above, the UE may perform frequency hopping of the SRS soas to transmit the SRS with the overall uplink data transmissionbandwidth. Such frequency hopping is set by a parameter b_(hop) having avalue of 0 to 3 received from a higher layer.

If frequency hopping of the SRS is deactivated, that is, ifb_(hop)≧B_(SRS), a frequency position index n_(b) has a constant valueas shown Equation 7. Here, n_(RRC) is a parameter received from a higherlayer.

n _(b)=└4n _(RRC) /m _(SRS,b)┘ mod N _(b)  Equation 7

Meanwhile, if frequency hopping of the SRS is activated, that is,b_(hop)<B_(SRS), a frequency position index n_(b) is defined byEquations 8 and 9.

$\begin{matrix}{n_{b} = \left\{ \begin{matrix}{\left\lfloor {4\; {n_{RRC}/m_{{SRS},b}}} \right\rfloor {mod}\; N_{b}} & {b \leq b_{hop}} \\{\left\{ {{F_{b}\left( n_{SRS} \right)} + \left\lfloor {4\; {n_{RRC}/m_{{SRS},b}}} \right\rfloor} \right\} {mod}\; N_{b}} & {otherwise}\end{matrix} \right.} & {{Equation}\mspace{14mu} 8} \\{{F_{b}\left( n_{SRS} \right)} = \left\{ \begin{matrix}\begin{matrix}{{\left( \frac{N_{b}}{2} \right)\left\lfloor \frac{n_{SRS}{mod}\; {\prod\limits_{b^{\prime} = b_{hop}}^{b}\; N_{b^{\prime}}}}{\prod\limits_{b^{\prime} = b_{hop}}^{b - 1}\; N_{b^{\prime}}} \right\rfloor} +} \\\left\lfloor \frac{n_{SRS}{mod}\; {\prod\limits_{b^{\prime} = b_{hop}}^{b}\; N_{b^{\prime}}}}{2{\prod\limits_{b^{\prime} = b_{hop}}^{b - 1}\; N_{b^{\prime}}}} \right\rfloor\end{matrix} & {{if}\mspace{14mu} N_{b}\mspace{14mu} {even}} \\{\left\lfloor \frac{N_{b}}{2} \right\rfloor \left\lfloor \frac{n_{SRS}}{\prod\limits_{b^{\prime} = b_{hop}}^{b - 1}\; N_{b^{\prime}}} \right\rfloor} & {{if}\mspace{14mu} N_{b}\mspace{14mu} {odd}}\end{matrix} \right.} & {{Equation}\mspace{14mu} 9}\end{matrix}$

where, n_(SRS) is a parameter used to calculate the number of times oftransmission of the SRS and is defined by Equation 10.

$\begin{matrix}{n_{SRS} = \left\{ \begin{matrix}{\begin{matrix}{{2\; N_{SP}n_{f}} + {2\left( {N_{SP} - 1} \right)\left\lfloor \frac{n_{s}}{10} \right\rfloor} +} \\\left\lfloor \frac{T_{offset}}{T_{offset\_ max}} \right\rfloor\end{matrix},} & \begin{matrix}{{for}\mspace{14mu} 2\mspace{11mu} {ms}\mspace{14mu} {SRS}\mspace{14mu} {periodicity}} \\{{of}\mspace{14mu} {TDD}\mspace{14mu} {frame}\mspace{14mu} {structure}}\end{matrix} \\{\left\lfloor {\left( {{n_{f} \times 10} + \left\lfloor {n_{s}/2} \right\rfloor} \right)/T_{SRS}} \right\rfloor,} & {otherwise}\end{matrix} \right.} & {{Equation}\mspace{14mu} 10}\end{matrix}$

In Equation 10, T_(SRS) denotes the periodicity of an SRS and T_(offset)denotes a subframe offset of an SRS. In addition, n_(s) denotes a slotnumber and n_(f) denotes a frame number.

A UE-specific SRS configuration index I_(SRS) for setting theperiodicity T_(SRS) and the subframe offset T_(offset) of a UE-specificSRS signal is shown in Tables 5 and 6 according to FDD and TDD. Inparticular, Table 5 shows the SRS configuration index for FDD and Table6 shows the SRS configuration index for TDD.

TABLE 5 SRS Configuration Index SRS Periodicity T_(SRS) SRS SubframeI_(SRS) (ms) Offset T_(offset) 0-1 2 I_(SRS) 2-6 5 I_(SRS) − 2  7-16 10I_(SRS) − 7 17-36 20 I_(SRS) − 17 37-76 40 I_(SRS) − 37  77-156 80I_(SRS) − 77 157-316 160 I_(SRS) − 157 317-636 320 I_(SRS) − 317 637-1023 reserved reserved

TABLE 6 Configuration Index SRS Periodicity T_(SRS) SRS Subframe I_(SRS)(ms) Offset T_(offset) 0 2 0, 1 1 2 0, 2 2 2 1, 2 3 2 0, 3 4 2 1, 3 5 20, 4 6 2 1, 4 7 2 2, 3 8 2 2, 4 9 2 3, 4 10-14 5 I_(SRS) − 10 15-24 10I_(SRS) − 15 25-44 20 I_(SRS) − 25 45-84 40 I_(SRS) − 45  85-164 80I_(SRS) − 85 165-324 160 I_(SRS) − 65 325-644 320 I_(SRS) − 325 645-1023 reserved reserved

As described above, the UE receives parameters from the eNB through RRCsignaling and transmits a periodic SRS. In contrast, the eNB instructsthe UE to transmit an aperiodic SRS and the UE transmits the aperiodicSRS to the eNB according to the instruction.

Unlike the periodic SRS defined in the LTE system, if transmission of anaperiodic SRS is additionally instructed using L1/L2 control signaling,the additionally transmitted aperiodic SRS may be configured to betransmitted once or a restricted number of times or may be configured tobe transmitted with predetermined periodicity. Control signaling whichmay be transmitted one time or a restricted number of times may be RRCsignaling or L1 control signaling or may be predefined between the UEand the eNB so as to prevent additional overhead for additionalsignaling. Information about a subframe or subframe group via which anSRS is transmitted may also be included in L1/L2 control signaling.

In transmission of an aperiodic SRS, a symbol via which an additionalSRS is transmitted may be configured to be allocated to the samesubframe as a subframe to which the periodic SRS is allocated or asubframe different from the subframe to which the periodic SRS isallocated. A method of allocating the symbol to the subframe differentfrom the subframe to which the periodic SRS is allocated refers to amethod of setting a transmit interval of a symbol allocated to anaperiodic SRS to a subset of UE-specific SRS periodicity, that is, 2 ms,4 ms, 5 ms, 10 ms or 20 ms which is a multiple of periodicity, whenUE-specific SRS periodicity defined in the conventional LTE system is 1ms.

More specifically, in the conventional LTE system, a subframe via whichan SRS is periodically transmitted has a cell-specific configuration. Asdescribed above, if the symbol for the additionally transmittedaperiodic SRS is configured to be allocated to the same subframe as acell-specific subframe to which the periodic SRS is allocated, theadditionally transmitted SRS may have the same configuration as thecell-specific configuration or a subset of subframes which areconfigured to periodically transmit the SRS may be allocated for theadditionally transmitted SRS.

That is, the additional SRS indicated by L1/L2 control signaling may betransmitted via a symbol reserved for transmitting the periodic SRS in asubframe via which the periodic SRS may be transmitted, another symbolreserved for transmitting the aperiodic SRS, or a symbol allocated orreserved for transmitting an uplink DM-RS.

The aperiodic SRS may be configured to be transmitted only via apredetermined cell-specific subframe configured to transmit the existingSRS and PUSCH puncturing is performed only in the predeterminedcell-specific subframe so as to minimize uplink data throughput loss.

As parameters of the aperiodic SRS, resources used to transmit theperiodic SRS, e.g., a cell-specific SRS bandwidth configuration, aUE-specific SRS bandwidth configuration, a frequency start position, atransmissionComb parameter, etc. may be used.

Alternatively, the parameters of the aperiodic SRS may be used as an RRCcontrol signal similarly to a method used to transmit the periodic SRS,and an additional SRS may be transmitted using resources used totransmit the additional SRS, e.g., a cell-specific SRS bandwidth, aUE-specific SRS bandwidth, a frequency start position, atransmissionComb, etc.

Alternatively, the aperiodic SRS may be transmitted using an entirebandwidth usable in a system bandwidth, regardless of a cell-specificSRS bandwidth configuration and a UE-specific SRS bandwidthconfiguration. For example, an SRS occupying 24 RBs may be transmittedif a system bandwidth is 5 MHz, an SRS occupying 48 RBs may betransmitted if a system bandwidth is 10 MHz, an SRS occupying 72 RBs maybe transmitted if a system bandwidth is 15 MHz, and an SRS occupying 96RBs may be transmitted if a system bandwidth is 20 MHz.

Meanwhile, time resources used to transmit the aperiodic SRS, that is, asubframe position, follows a configuration included in downlink controlinformation (DCI) or the aperiodic SRS may be transmitted via a subframehaving a specific relationship. Hereinafter, a method of signalingtransmission of an aperiodic SRS will be described.

First, a method of signaling an instruction to transmit an aperiodic SRSin a DCI format for uplink transmission may be considered. That is, ifan eNB signals an instruction to transmit the aperiodic SRS via ann^(th) subframe in the DCI format for uplink transmission, a UE maydecode the received uplink DO format and transmit the aperiodic SRS tothe eNB via an (n+k)^(th) subframe (k≧4).

However, in the case of a TDD system, an (n+k)^(th) subframe may not bean uplink subframe. If collision with a periodic SRS occurs,transmission of the aperiodic SRS may not be ensured.

Accordingly, a method of signaling an instruction to transmit theaperiodic SRS in a DCI format for downlink transmission is morepreferable. In general, since the number of times of decoding the DCIformat for downlink transmission at the UE is greater than the number oftimes of decoding of the DCI format for uplink transmission, the UE mayefficiently cope with a sounding request of the base station.

First, if the eNB instructs only triggering/release oractivation/deactivation signaling of the aperiodic SRS in a downlink DCIformat, the amount of signaling information is not large, an unusedinformation bit or bits in the DCI format for downlink transmission usedin the LIE system or a combination of specific code points usable in theDCI format for downlink transmission may be used. In this case, theparameters of the SRS may be signaled through a higher layer, that is,an RRC layer, in advance. In addition, an aperiodic SRS does not satisfybackward compatibility for the LTE system, the aperiodic SRS may not beused in the LTE system, that is, Rel-8/9, but may be used in the LTE-Asystem, that is, subsequent Releases of Rel-10. A method of using a DCIformat for downlink transmission newly defined in the LIE-A system maybe used. For example, a method of using a DCI format for downlinktransmission for an 8×8 MIMO system newly defined in Rel-10 may beconsidered.

In addition, even if all parameters for SRS transmission as well astriggering/release or activation/deactivation of the aperiodic SRS aredynamically signaled using DCI for downlink transmission, under thecondition that a PDSCH is not transmitted in downlink, an unusedinformation bit or bits in a DCI format for downlink transmission usedin the LTE system or a combination of specific code points in the DCIformat for downlink transmission may be used. In this case, allparameters for the UE-specific SRSs among the above-described SRSs orparameters of a subset of UE-specific parameters, e.g., cyclic shift(CS), transmissionComb and a UE-specific SRS bandwidth, may bedynamically signaled using a DCI format for downlink transmission andthe remaining UE-specific parameters and the cell-specific parameters ofthe above-described SRSs may be signaled in advance through a higherlayer, that is, an RRC layer. In this case, a method of using a DCIformat for downlink transmission newly defined in the LTE-A system maybe considered. For example, a method of using a DCI format for downlinktransmission for an 8×8 MIMO system newly defined in Rel-10 may beconsidered. For example, the DCI format for downlink transmission newlydefined in the LTE-A system, for example, a DCI format for downlinktransmission for an 8×8 MIMO system may be used.

FIG. 6 is a block diagram showing a transmitter or receiver according toan embodiment of the present invention. The transmitter or receiver maybe a part of an eNB or a UE.

Referring to FIG. 6, a transmitter/receiver 600 includes a processor610, a memory 620, a Radio Frequency (RF) module 630, a display module640 and a user interface module 650.

The transmitter/receiver 600 is shown for convenience of description andsome modules thereof may be omitted. In addition, thetransmitter/receiver 600 may further include necessary modules. Inaddition, some modules of the transmitter/receiver 600 may besubdivided. The processor 610 is configured to perform an operation ofthe embodiment of the present invention described with respect to thedrawings.

More specifically, if the transmitter/receiver 600 is a part of an eNB,the processor 610 may perform a function for generating a control signaland mapping the control signal to a control channel set within aplurality of frequency blocks. If the transmitter/receiver 600 is a partof a UE, the processor 610 may confirm a control channel indicatedthereto from a signal received through a plurality of frequency blocksand extract a control signal therefrom.

Thereafter, the processor 610 may perform a necessary operation based onthe control signal. For a detailed description of the operation of theprocessor 610, reference may be made to the description associated withFIGS. 1 to 5.

The memory 620 is connected to the processor 610 so as to store anoperating system, an application, program code, data and the like. TheRF module 630 is connected to the processor 610 so as to perform afunction for converting a baseband signal into a radio signal orconverting a radio signal into a baseband signal. The RE module 630performs analog conversion, amplification, filtering and frequencyup-conversion or inverse processes thereof. The display module 640 isconnected to the processor 610 so as to display a variety ofinformation. As the display module 640, although not limited thereto, awell-known device such as a Liquid Crystal Display (LCD), a LightEmitting Diode (LED), or an Organic Light Emitting Diode (OLED) may beused. The user interface module 650 is connected to the processor 610and may be configured by a combination of well-known user interfacessuch as a keypad and a touch screen.

The above-described embodiments are proposed by combining constituentcomponents and characteristics of the present invention according to apredetermined format. The individual constituent components orcharacteristics should be considered to be optional factors on thecondition that there is no additional remark. If required, theindividual constituent components or characteristics may not be combinedwith other components or characteristics. Also, some constituentcomponents and/or characteristics may be combined to implement theembodiments of the present invention. The order of operations to bedisclosed in the embodiments of the present invention may be changed toanother. Some components or characteristics of any embodiment may alsobe included in other embodiments, or may be replaced with those of theother embodiments as necessary. Moreover, it will be apparent that someclaims referring to specific claims may be combined with another claimsreferring to the other claims other than the specific claims toconstitute the embodiment or add new claims by means of amendment afterthe application is filed.

The above-mentioned embodiments of the present invention are disclosedon the basis of a data communication relationship between a base stationand a user equipment. Specific operations to be conducted by the basestation in the present invention may also be conducted by an upper nodeof the base station as necessary. In other words, it will be obvious tothose skilled in the art that various operations for enabling the basestation to communicate with the user equipment in a network composed ofseveral network nodes including the base station will be conducted bythe base station or other network nodes other than the base station. Theterm “Base Station” may be replaced with the terms fixed station,Node-B, eNode-B (eNB), or access point as necessary. The term “terminal”may also be replaced with the term user equipment (UE), subscriberstation (SS) or mobile subscriber station (MSS) as necessary.

The embodiments of the present invention can be implemented by a varietyof means, for example, hardware, firmware, software, or a combinationthereof. In the case of implementing the present invention by hardware,the present invention can be implemented through application specificintegrated circuits (ASICs), Digital signal processors (DSPs), digitalsignal processing devices (DSPDs), programmable logic devices (PLDs),field programmable gate arrays (FPGAs), a processor, a controller, amicrocontroller, a microprocessor, etc.

If operations or functions of the present invention are implemented byfirmware or software, the present invention can be implemented in theform of a variety of formats, for example, modules, procedures,functions, etc. The software codes may be stored in a memory unit so asto be driven by a processor. The memory unit may be located inside oroutside of the processor, so that it can communicate with theaforementioned processor via a variety of well-known parts.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

The present invention is applicable to a wireless communication systemand, more particularly, to a method and apparatus for transmitting asounding reference signal in a wireless communication system to whichcarrier aggregation is applied.

What is claimed is:
 1. A method for receiving an aperiodic soundingreference signal (SRS) from a user equipment (UE) at a base station in atime division duplex (TDD) communication system, the method comprising:transmitting downlink control information (DCI) including a request ofthe aperiodic SRS to the UE, wherein the downlink control informationincludes information for receiving downlink data using multiple antennasfrom the base station by the user equipment; and receiving the aperiodicSRS from the UE in response to the request.
 2. The method according toclaim 1, wherein, if the downlink control information is transmitted onan nth subframe, the aperiodic SRS is received on an (n+k)th subframe(k≧4).
 3. The method according to claim 1, further comprising:configuring at least one parameter for the aperiodic SRS through a RadioResource Control (RRC) layer to the UE, wherein the aperiodic SRS istransmitted using the at east one parameter.
 4. The method according toclaim 3, wherein the at least one parameter includes information on atleast one of a bandwidth for the aperiodic SRS, a frequency startposition for the aperiodic SRS, and a transmissionComb for the aperiodicSRS.
 5. A base station in a time division duplex (TDD) communicationsystem, the base station comprising: a transmission module configured totransmit downlink control information (DCI) including a request of anaperiodic sounding reference signal (SRS) to the UE, wherein thedownlink control information includes information for receiving downlinkdata using multiple antennas from the base station by the userequipment; and a reception module configured to receive the aperiodicSRS from the UE in response to the request.
 6. The base stationaccording to claim 5, wherein, if the downlink control information istransmitted on an nth subframe, the aperiodic SRS is received on an(n+k)th subframe (k≧4).
 7. The base station according to claim 5,further comprising: configuring at least one parameter for the aperiodicSRS through a Radio Resource Control (RRC) layer to the UE, wherein theaperiodic SRS is transmitted using the at least one parameter.
 8. Thebase station according to claim 7, wherein the at least one parameterincludes information on at least one of a bandwidth for the aperiodicSRS, a frequency start position for the aperiodic SRS, and atransmissionComb for the aperiodic SRS.